Mid-Level Clouds over the Southeast Atlantic

The southeast Atlantic is home to mid-level clouds, occurring either near the top of the moist free-tropospheric smoke plume, or embedded within it. The mid-level clouds will alter local radiative profiles and generate remote sensing biases if they are mis-classified as a low cloud. Here we use a combination of remotely-sensed data (primarily air- and space-borne lidar, MeteoSat cloud retrievals, and reanalysis) to better understand the presence of the mid-level clouds during August to October. We find that passive satelite remote sensors underestimate the height of the mid-level clouds, more so when the underlying low cloud fraction is high. The mid-level clouds, through their small cloud-top effective radii, encourage high satellite-derived cloud droplet number concentration estimates. The mid-level clouds are as likely to occur embedded in the smoke acloud as located near the plume top, consistent with a strongly coupled aerosol and moisture layering. This also suggests the mid-level clouds help maintain themi mixed layers, but do not necessarily deepen them. Moisture fluxes and convergence explain the annual cycle in mid-level cloudiness, and climatologically are more common when deep convection is occurring on the continental Africa.